This invention relates generally to air conditioning systems. More particularly the invention relates to an air conditioning system having an axial flow fan for moving air through a refrigerant condenser.
Warm air is frequently also humid, i.e. it contains entrained water vapor. During operation of an air conditioning system in the cooling mode, the system refrigerant evaporator reduces the temperature of the air passing through it to below the dewpoint. In that condition, water vapor condenses on the evaporator. Some means must be provided to dispose of this condensate. In small unitary air conditioners, such as window or though-the-wall mounted room air conditioners, a common means to accomplish condensate disposal is by providing a condensate collection and drain path that communicates between the inside section and the outside section of the air conditioner. Condensate formed on the system evaporator drains into a collector in the inside section and then flows to a collector located under the condenser fan in the outside section. The outside section condensate collector and the condenser fan are arranged so that the fan will contact the condensate in the collector and sling it on to the hot surfaces of the system condenser where the condensate water evaporates. The arrangement is such that the fan will sling the condensate before the water in the collector rises to a level where it can overflow. A slinger arrangement eliminates the need for an inconvenient, unsightly and costly condensate drain from the air conditioner. There is another benefit from such an arrangement, in that the heat necessary to evaporate the water is taken from and thus assists in cooling the warm refrigerant in the condenser, resulting in an improvement in system efficiency.
Some prior art designs provide condensate slinging capability in a fan by incorporating a shroud or ring as part of the fan. The shroud encircles the fan blades and attaches to each blade at its tip. The shroud contacts the water when the condensate reaches the design level, lifting the water into the moving air stream produced by the fan and causing the water to pass into the condenser.
Condensate disposal arrangements using fans with slinger rings have certain design and performance shortcomings. Not all the water lifted from the condensate collector by the slinger ring is carried into the fan discharge. Some, in the form of droplets, is thrown radially outward until it impacts the system enclosure or other structural components. The impact of the droplets can cause annoying noise. Further, the condensate that does not spray upon the exterior of the condenser tubes is not available to increase the thermal efficiency of the system. Several prior art inventions have dealt with these problems by fitting stationary shrouds around the ringed fan. These stationary shrouds were configured to prevent the impingement of condensate droplets on other system structures and direct the droplets on to the condenser. Hence the configuration of the stationary shrouds were not able to be optimized for other considerations such as fan air flow efficiency and noise reduction.
Encircling a fan with a rotating shroud or ring affixed to it also creates design and manufacturing difficulties, particularly when the fan is made of plastic in one piece. Since the shroud is at the region of maximum rotational velocity, the centrifugal force resulting from its weight is at a maximum for a given fan geometry, requiring that other portions of the fan be made to have the strength necessary to withstand the force generated by the shroud. This requirement may mean that the fan construction must be more robust than would otherwise be required. The junctions where the shroud meets and joins to the tips of the blades can be areas of weakness just where maximum strength is required. Plastic one piece fans are commonly manufactured using an injection molding process, with the point of plastic material injection into the fan mold being in the central or hub area. Achieving a good mold fill on a shrouded fan design can be difficult. In a molded plastic shrouded fan, a zone of reduced strength can be present in the shroud ring at a location equidistant or nearly so from adjacent fan blades because at that location, flows of plastic from opposite directions meet during the molding process but fail to meld and knit properly and completely.